The body's healing response to wounds includes the formation of scar tissue. This response occurs in the vascular system after injury or trauma such as may be caused by angioplasty or other similar treatments thereby resulting in a condition commonly referred to as restenosis. As a result of restenosis, scar tissue grows on the inner walls of the vessels vascular system thereby causing an undesirable narrowing of the vessels. Accordingly, it is desirable to prevent or inhibit restenosis as part of the overall treatment of the vascular system following procedures such as angioplasty or the like. While angioplasty currently has a short-term success rate of 90–95%, due to restenosis, about 30–50% of patients' vessels narrow to approximately 50% or less of the size of the native vessel.
A variety of different therapies for the prevention of restenosis have been employed including light therapies, chemotherapeutic agents, stents, atherectomy devices and lasers. One method for preventing or inhibiting restenosis which has shown promise is the irradiation the inner vascular wall subsequent to the treatment in order to prevent or inhibit scar tissue formation, sometimes referred to as intimal hyperplasia. However, the devices for delivery of radiation sources to the treatment site suffer from a number of drawbacks which limit their usefulness and effectiveness.
U.S. Pat. No. 5,084,002 (Liprie) relates to an ultra-thin, high dose iridium source for remote treatment of cancerous tissue with radiation. This device is specifically designed for use in areas of the human body where minimization of trauma to adjacent tissue is a high priority. As a result, the radioactive source is encapsulate in a thin platinum delivery wire with an ultra-thin cross section. A similar device is also disclosed in U.S. Pat. No. 5,141,487 (Liprie).
U.S. Pat. No. 5,302,168 (Hess) relates to a method and apparatus for restenosis treatment after angioplasty by application of a radioactive dose to the reduced region of the artery. In one embodiment disclosed in this patent, a radioactive dose is positioned in a housing at the distal end of a catheter delivery device. The housing is provided with a window cut-out covered by a sheath. The sheath is drawn back when the radioactive dose means is positioned for treatment. A second embodiment disclosed in this patent involves attaching radioactive elements to an angioplasty balloon catheter and expanding the balloon in the area to be treated to force the radioactive elements into contact with the area to be treated.
U.S. Pat. No. 5,213,561 (Weinstein et al.) discloses methods and devices for preventing restenosis after angioplasty. More specifically, various embodiments are disclosed wherein a radioactive source is mounted at the end of a guide wire, is delivered inside a tube provided with a guide wire in a balloon catheter or is coated on a balloon expandable stent. A retractable sheath is employed to enclose the radiation source until irradiation is desired at which point the sheath is retracted.
U.S. Pat. No. 5,199,939 (Dake) discloses a radioactive catheter and a method for using the catheter for preventing restenosis after angioplasty. The method includes employing an elongate, flexible catheter with a radioactive source located in its distal end to irradiate the treatment zone. The radioactive catheter employs a plurality of cylindrical radioactive pellets disposed among a plurality of cylindrical spacers as the radioactive source.
The foregoing embodiments suffer from a number of drawbacks. For example, many of the devices include a number of elements located between the radiation source and the area to be treated which results in shielding which may reduce the effect of the radiation and/or cause an irregular distribution of the radiation dose. Other devices provide the radioactive source material in a plurality of discrete elements which inherently results in different levels of radiation dose being applied to different parts of the treated area. Other drawbacks of specific devices exist as well.